Olefin oligomerization process

ABSTRACT

In a process for oligomerizing a C 2  to C 6  n-olefin feedstock over surface deactivated ZSM-23, the feedstock contains from about 0.1 wt % to about 25 wt % of an iso-olefin and the C 12 + fraction of the oligomerized olefin product contains less than 0.5 atom % of quaternary carbon atoms.

FIELD

This invention relates to a process for oligomerizing a lower molecularweight olefin to produce a higher molecular weight olefin mixture, morespecifically a substantially linear olefinic hydrocarbon mixture.

BACKGROUND

Long chain olefins (C₁₀+) are important starting materials in theproduction of sulfonate surfactants, in which the olefins are used toalkylate aromatic hydrocarbons and the resultant alkyl aromatics aresulfonated to produce alkylaryl sulfonates. In addition, the alcohols oflong chain olefins have considerable commercial importance in a varietyof applications, including detergents, soaps, surfactants, and freezepoint depressants in lubricating oils. In such applications, it isimportant that the olefins employed are substantially free of quaternarycarbon atoms because materials containing quaternary carbon atoms areresistant to biodegradation.

One potential route for the production of long chain olefins is by theoligomerization of lower (C₂ to C₆) olefins, typically using an acidiccatalyst, such as a zeolite. Thus, for example, it is known from U.S.Pat. Nos. 3,960,978, 4,150,062; 4,211,640; 4,227,992; and 4,547,613 tooligomerize lower olefins over ZSM-5.

U.S. Pat. Nos. 4,855,527; 4,870,038 and 5,026,933 describe a process forproducing high molecular weight, slightly branched hydrocarbon oligomersfrom a lower olefin feedstock employing a shape selective crystallinesilicate catalyst, ZSM-23, which has been surface deactivated. Theresultant oligomer mixture comprises at least 20% by weight of olefinshaving at least 12 carbon atoms and an average of from 0.8 to 2.0branches per carbon chain.

U.S. Pat. No. 5,284,989 is directed to a process for producingsubstantially linear hydrocarbons by oligomerizing a lower olefin atelevated temperature and pressure in the presence of an acidicaluminosilicate zeolite selected from ZSM-22, ZSM-23 and ZSM-35 whichhas been surface-deactivated by contacting with oxalic acid.

In view of the need to avoid the production of quaternary carbon atomsin the resultant olefin oligomers, it is normal to employoligomerization feeds which consist essentially of n-olefins and whichare substantially free of iso-olefins, such as iso-butylene andiso-amylene. This poses a problem in that one source of lower olefins ina modem integrated oil refinery is the unreacted effluent stream fromthe MTBE (methyl tertiary butyl ether) production unit, which streaminherently contains up to 5 wt % of iso-butylene. Thus, existingoligomerization processes either avoid the use of the MTBE effluent feedor else require expensive purification steps to remove the iso-olefins.

In accordance with the invention, it has now surprisingly been foundthat, when surface deactivated ZSM-23 is used to oligomerize a lowerolefin feed containing significant quantities of iso-olefins, such asthe unreacted effluent from an MTBE unit, the C₁₂+ product issubstantially free of quaternary carbon atoms. Instead, it is found thatany quaternary carbon-containing materials are concentrated in the C₈fraction, which can then be removed for use as a high-octane gasolineproduct. Although the reason for this desirable result is not fullyunderstood, it is believed that the size of the pores of the ZSM-23 aresuch that, although iso-butylene can enter the pores to react with, forexample, n-butylene, the resultant branched C₈ oligomer is too large toaccess the pores for further reaction.

SUMMARY

Accordingly, the invention resides in a first aspect in an olefinoligomerization process comprising:

(a) contacting a feedstock comprising one or more C₂ to C₆ n-olefins andfrom about 0.1 wt % to about 25 wt % of an iso-olefin underoligomerization conditions with surface-deactivated ZSM-23 to produce anoligomerized olefin product; and

(b) separating from said oligomerized olefin product a C₁₂+ fractioncontaining less than 0.5 atom % of quaternary carbon atoms.

In one embodiment, said feedstock contains about 0.5 wt % to about 5 wt% of said iso-olefin.

Typically, said iso-olefin is selected from iso-butylene andiso-amylene.

Conveniently, the n-olefin in the feedstock is selected from propylene,n-butene and mixtures thereof.

In one embodiment, the feedstock is the unreacted effluent stream froman MTBE unit.

Conveniently, the feedstock contains less than 100 ppm of dimethyl etherand has a sulfur content of less than 10 ppm.

Conveniently, the ZSM-23 has been surface deactivated with a stericallyhindered nitrogenous base, such as 2,4,6-collidine.

In a second aspect, the invention resides in a process for producing along chain alcohol mixture comprising contacting said C₁₂+ fraction withcarbon monoxide and hydrogen under hydroformylation conditions and inthe presence of a hydroformylation catalyst.

In a third aspect, the invention resides in a process for producing analkylaromatic compound comprising contacting an aromatic compound withsaid C₁₂+ fraction under alkylation conditions and in the presence of analkylation catalyst.

In a fourth aspect, the invention resides in a process for preparing analkylaryl sulfonate by sulfonating the alkylaromatic compound producedin accordance with said third aspect of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention provides an improved process for producingslightly branched, high molecular weight olefinic hydrocarbons byoligomerizing a lower olefinic hydrocarbon feedstock in the presence ofa surface-deactivated ZSM-23 catalyst. The use of such a catalyst isfound, unexpectedly, to allow the use of an olefin feedstock thatcontains significant quantities of iso-olefins, such as isobutylene,without producing deleterious quantities of quaternary carbon atoms inthe C₁₂+ fraction.

The olefinic hydrocarbon feedstock used in the process of the inventioncomprises one or more C₂ to C₆ n-olefins, such as propane and/orn-butene. In addition, the feedstock contains about 0.1% to about 25%,such as about 0.5% to 5% of an iso-olefin by weight of the totalfeedstock. Typically, the iso-olefin will be iso-butylene and/oriso-amylene. One preferred olefinic feedstock for use in the process ofthe invention is the unreacted effluent stream from an MTBE productionunit, which stream typically contains n-butene together withiso-butylene in amounts up to 5 wt %. A practical feedstock, such as anMTBE effluent, may also contain dimethyl ether and sulfur impurities. Ifpresent, the dimethyl ether content is preferably less than 100 ppm andthe sulfur content is preferably less than 10 ppm.

The olefinic hydrocarbon feedstock can also contain low molecularweight, typically C₄-C₆, saturated hydrocarbons, typically in amountsbetween about 5% and about 70% by weight of the overall feedstock.

The oligomerization catalyst used in the process of the inventioncomprises ZSM-23 which has been surface deactivated, typically bytreatment with a sterically hindered nitrogenous base, such as atrialkyl pyridine compound, and preferably with 2,4,6-collidine(2,4,6-trimethyl pyridine, gamma-collidine). The surface deactivatingcompound should have a minimum cross-sectional diameter greater than theeffective pore size of the zeolite to be treated; i.e., greater than 5Angstroms. ZSM-23 and its characteristic X-ray diffraction pattern aredescribed in detail in U.S. Pat. No. 4,076,842. Preferably, the ZSM-23employed in the catalyst has an alpha value of about 25 and a crystalsize of less than 0.1 micron and is conveniently composited with abinder, such as alumina.

Suitable oligomerization conditions include a temperature of about 160°C. to about 250° C., such as about 190° C. to about 230° C., for exampleabout 210° C. to about 220° C.; a pressure in the range of about 500psig (3447 kPa (gauge)) to about 1500 psig (10342 kPa (gauge)), such asin the range of about 750 psig (5171 kPa (gauge)) to about 1250 psig(8618 kPa (gauge)), and a feed weight hour space velocity (WHSV) in therange of about 0.1 hr⁻¹ to about 4.0 hr⁻¹, such as in the range of about0.2 hr⁻¹ to about 3.0 hr⁻¹, for example in the range of about 1.75 hr⁻¹to about 2.25 hr⁻¹.

Where surface deactivation is achieved by treatment with a trialkylpyridine compound, the feed to the oligomerization process can includeadditional trialkyl pyridine compound so that the surface properties ofthe zeolite are maintained during the process. Further details of theoligomerization process can be found in U.S. Pat. No. 5,026,933.

The product of the oligomerization process of the invention is anolefinic hydrocarbon mixture which comprises at least 5 wt %, such as atleast 20 wt %, for example at least 85 wt % of mono-olefin oligomers ofthe empirical formula:C_(n)H_(2n)wherein n is greater than or equal to 6 and wherein said mono-olefinoligomers comprise at least 20 wt %, and conveniently at least 60 wt %,of olefins having at least 12 carbon atoms and said olefins having atleast 12 carbon atoms (C₁₂+ olefins) have an average of from about 0.8to about 2.0, such as from about 0.8 to about 1.3, C₁-C₃ alkyl branchesper carbon chain. Conveniently, the olefins having at least 12 carbonatoms contain no branches other than methyl and ethyl groups.

In particular it is found that, despite the presence of iso-olefins inthe oligomerization feed, the C₁₂+ olefinic product of the presentprocess contains less than 0.5 atom %, of quaternary carbon atoms. Aspreviously stated, although the reasons for the low quaternary carboncontent of the C₁₂+ olefinic product are not fully understood, it isbelieved that the size of the pores of the ZSM-23 are such that,although iso-butylene can enter the pores to react with, for example,n-butylene, the resultant branched C₈ oligomer is too large to accessthe pores for further reaction. Thus the iso-olefin reaction productsare concentrated, in the case of a C₄ olefin feed, in the C₈ fraction.Because such a fraction inherently has a high octane value, it isadvantageous to remove this fraction from the oligomerization productfor use as a gasoline blending component.

The percentage of quaternary carbon atoms in the C₁₂+ olefinic productis conveniently determined by the ¹³C—NMR technique described in U.S.Pat. No. 5,849,960 at column 4, line 23 to column 5, line 3 and inparticular the J-Modulated Spin Echo NMR technique (JMSE) using a ½Jdelay of 4 ms and incorporating the DEPT-135 NMR correction.

The lightly branched C₁₂+ olefinic hydrocarbon fraction from theoligomerization process of the invention is conveniently used in theproduction of long chain alcohols for application as, for example,detergents, soaps, surfactants, and freeze point depressants inlubricating oils. Typically this is achieved by hydroformylation, thatis reaction with carbon monoxide and hydrogen, according to the Oxoprocess. Catalysts employed can be cobalt or rhodium which may bemodified with phosphine, phosphite, arsine or pyridine ligands, asdescribed in U.S. Pat Nos. 3,231,621; 3,239,566; 3,239,569; 3,239,570;3,239,571; 3,420,898; 3,440,291; 3,448,158; 3,448,157; 3,496,203; and3,496,204; 3,501,515; and 3,527,818.

Typical hydroformylation reaction conditions include a temperature ofabout 125° C. to about 200° C., a pressure of about 2170 kPa to about32550 kPa (300 psig to 4000 psig) and a catalyst to olefin ratio ofabout 1:5000 to about 1:1. The molar ratio of hydrogen to carbonmonoxide is usually about 0.5 to about 10, such as about 1 to about 2.The hydroformylation reaction typically produces an aldehyde which canthen be hydrogentated to generate the required alcohol product.

The hydroformylation process can be carried out in the presence of aninert solvent, such as a ketone, e.g., acetone, methyl ethyl ketone,methyl isobutyl ketone, acetophenone, and cyclohexanone; an aromaticcompound, e.g., benzene, toluene and the xylenes; a halogenated aromaiccompound, e.g., chlorobenzene and orthodichlorobenzene; a halogenatedparaffinic hydrocarbon, e.g., methylene chloride and carbontetrachloride; a paraffin, e.g., hexane, heptane, methylcyclohexane andisooctane, and a nitrile, e.g., such as benzonitrile and acetonitrile.

The catalyst ligand may be made of tertiary organo phosphines, such astrialkyl phosphines, triamyl phosphine, trihexyl phosphine, dimethylethyl phosphine, diamylethyl phosphine, tricyclopentyl (or hexyl)phosphine, diphenyl butyl phosphine, dipenyl benzyl phosphine, triethoxyphosphine, butyl diethyoxy phosphine, triphenyl phosphine, dimethylphenyl phosphine, methyl diphenyl phosphine, dimethyl propyl phosphine,the tritolyl phosphines and the corresponding arsines and stibines.Included as bidentate-type ligands are tetramethyl diphosphinoethane,tetramethyl diphosphinopropane, tetraethyl diphosphinoethane, tetrabutyldiphosphinoethane, dimethyl diethyl diphosphinoethane, tetraphenyldiphosphinoethane, tetraperfluorophenyl diphosphinoethane, tetraphenyldiphosphinopropane, tetraphenyl diphosphinobutane, dimethyl diphenyldiphosphinoethane, diethyl diphenyl diphosphinopropane and tetratrolyldiphosphinoethane.

Examples of other suitable ligands are the phosphabicyclohydrocarbons,such as 9-hydrocarbyl-9-phosphabicyclononane in which the smallestP-containing ring contains at least 5 carbon atoms. Some examplesinclude 9-aryl-9-phosphabicyclo[4.2.1]nonane,(di)alkyl-9-aryl-9-phosphabicyclo[4.2.1]nonane,9-alkyl-9-phosphabicyclo[4.2.1]nonane,9-cycloalkyl-9-phosphabicyclo[4.2.1]nonane,9-cycloalkenyl-9-phosphabicyclo[4.2.1]nonane, and their [3.3.1] and[3.2.1] counterparts, as well as their triene counterparts.

Alternatively, the lightly branched C₁₂+ olefinic hydrocarbon fractionfrom the oligomerization process of the invention can be used, eitheralone or in admixture with linear alpha-olefins, as an alkylating agentin a process for the selective alkylation of an aromatic compound (e.g.,benzene) with a relatively long chain length alkylating agent to producesubstantially linear phenylalkanes. The alkylation process is conductedsuch that the organic reactants, i.e., the aromatic compound and theolefinic hydrocarbon mixture, are contacted under effective alkylationconditions with a suitable acid catalyst. Suitable aromatic hydrocarbonsinclude benzene, toluene, xylene and naphthalene, with preferredcompounds being benzene and toluene.

In one embodiment, the catalyst is a homogeneous acid catalyst such as aLewis acid catalyst, for example aluminum chloride. Alternatively, thehomogeneous acid catalyst is a Brønsted acid catalyst such as HF orphosphoric acid. Suitable alkylation conditions with a homogeneouscatalyst include a temperature of from about −10° C. to about 100° C., apressure of from about 100 kPa to about 2500 kPa (1.0 to 25atmospheres), a feed weight hourly space velocity (WHSV) of from about0.2 hr⁻¹ to about 10 hr⁻¹ and an aromatic compound to olefinichydrocarbon mixture mole ratio of from about 1:1 to about 15:1. Typicalreaction conditions include a temperature of from about 0° C. to about50° C., a pressure of from about 100 kPa to about 300 kPa (1.0 to about3.0 atmospheres), a feed weight hourly space velocity (WHSV) of fromabout 0.1 hr⁻¹ to about 0.5 hr⁻¹ and an aromatic compound to olefinichydrocarbon mixture mole ratio of from about 5:1 to about 10:1. Thereactants can be in either the vapor phase or the liquid phase and canbe neat, i.e., free from intentional admixture or dilution with othermaterial, or they can be brought into contact with the catalystcomposition with the aid of carrier gases or diluents such as, forexample, hydrogen or nitrogen.

In a further embodiment, the alkylation process is conducted in thepresence of a heterogeneous catalyst, such as a molecular sieve.Suitable molecular sieves include mordenite, particularly dealuminizedmordenite and other 6-7 Angstrom pore molecular sieves disclosed in U.S.Pat. No. 5,026,933.

In one practical embodiment, the alkylation catalyst comprises amolecular sieve having an X-ray diffraction pattern including d-spacingmaxima at 12.4±0.25, 6.9±0.15, 3.57±0.07 and 3.42±0.07 Angstroms. TheX-ray deffraction data used to characterize said molecular sieve areobtained by standard techniques using the K-alpha doublet of copper asthe incident radiation and a diffractometer equipped with ascintillation counter and associated computer as the collection system.Materials having the required X-ray faction lines are sometimes referredto as molecular sieves of the MCM-22 family and include MCM-22(described in U.S. Pat. No. 4,954,325), PSH-3 (described in U.S. Pat.No. 4,439,409), SSZ-25 (described in U.S. Pat. No. 4,826,667), ERB-1 isdescribed in European Patent No. 0293032, ITQ-1 is described in U.S.Pat. No. 6,077,498, ITQ-2 is described in International PatentPublication No. WO97/17290, MCM-36 (described in U.S. Pat. No.5,250,277), MCM-49 (described in U.S. Pat. No. 5,236,575) and MCM-56(described in U.S. Pat. No. 5,362,697).

The molecular sieve alkylation catalyst can be combined in conventionalmanner with an oxide binder, such as alumina, such that the finalalkylation catalyst contains between about 2 and about 80 wt % sieve.

With a molecular sieve catalyst, suitable alkylation conditions includea temperature of from about 0° C. to about 500° C., a pressure of fromabout 20 kPa to about 25000 kPa (0.2 to 250 atmospheres), a feed weighthourly space velocity (WHSV) of from about 0.1 hr⁻¹ to about 500 hr⁻¹,and an aromatic compound to olefinic hydrocarbon mixture mole ratio offrom about 1:1 to about 20:1. The WHSV is based upon the weight of thecatalyst composition employed, i.e., the total weight of active catalyst(and binder if present). Typical reaction conditions include atemperature within the range of from about 100° C. to about 350° C., apressure of from about 100 kPa to about 2500 kPa (1 to 25 atmospheres),a WHSV of from about 0.5 hr⁻¹ to about 100 hr⁻¹ and an aromatic compoundto olefinic hydrocarbon mixture mole ratio of from about 4:1 to about15:1. Again, the reactants can be in either the vapor phase or theliquid phase and can be neat, i.e. free from intentional admixture ordilution with other material, or they can be brought into contact withthe zeolite catalyst composition with the aid of carrier gases ordiluents such as, for example, hydrogen or nitrogen.

The alkylation process of the invention produces an alkylaromatichydrocarbon mixture in which the alkyl side chains are lightly branchedand have less tan 0.5 atom % of quaternary carbon atoms and in whichmost of the aromatic species are located at the 2- or 3-position in thealkyl side chain. The alkylaromatic hydrocarbon mixture is thereforeparticularly useful as an intermediate in the production ofalkylarylsulfonates, which are useful as detergents or surfactants.Processes for sulfonating alkylbenzenes are described in the U.S. Pat.No. 4,298,547. More particularly, alkylaromatic hydrocarbons may beconverted to alkylarylsulfonates by sulfonation of the aromatic ringwith sulfuric acid. The sulfonation reaction is well known in the artand is commonly carried out by contacting the organic compound withsulfuric acid at temperatures of from about −70° C. to about +60° C.Detailed descriptions of specific commercial processes abound theliterature. See, for instance, pages 60-62 of INDUSTRIAL CHEMICALS,Third Edition, by W. L. Faith et al, published by John Wiley & Sons,Inc.

1. An olefin oligomerization process comprising: (a) contacting afeedstock comprising one or more C₂ to C₆ n-olefins and from about 0.1wt % to about 25 wt % of an iso-olefin under oligomerization conditionswith surface-deactivated ZSM-23 to produce an oligomerized olefinproduct; and (b) separating from said oligomerized olefin product a C₁₂+fraction containing less than 0.5 atom % of quaternary carbon atoms. 2.The process according to claim 1, wherein said feedstock contains about0.5 wt % to about 5 wt % of an iso-olefin.
 3. The process according toclaim 1, wherein said iso-olefin is iso-butylene and/or iso-amylene. 4.The process according to claim 1, wherein said one or more n-olefins inthe feedstock are selected from propylene, n-butene and mixturesthereof.
 5. The process according to claim 1, wherein said feedstock isthe unreacted effluent stream from an MTBE unit.
 6. The processaccording to claim 1, wherein said feedstock contains less than 100 ppmof dimethyl ether.
 7. The process according to claim 1, wherein saidfeedstock has a sulfur content of less than 10 ppm.
 8. The processaccording to claim 1, wherein said ZSM-23 has been surface deactivatedwith a sterically hindered nitrogenous base.
 9. The process according toclaim 8, wherein said sterically hindered nitrogenous base is2,4,6-collidine.
 10. The process according to claim 1, wherein saidoligomerization conditions include a temperature of about 160 to about250° C.
 11. The process according to claim 1, wherein saidoligomerization conditions include a temperature of about 190 to about230° C.
 12. The process according to claim 1, wherein saidoligomerization conditions include a temperature of about 210 to about220° C.
 13. The process according to claim 1, wherein saidoligomerization conditions comprise a pressure in the range of fromabout 500 psig (3447 kPa (gauge)) to about 1500 psig (10342 kPa(gauge)).
 14. The process according to claim 1, wherein saidoligomerization conditions comprise a pressure in the range of fromabout 750 psig (5171 kPa (gauge)) to about 1250 psig (8618 kPa (gauge)).15. The process according to claim 1, wherein said oligomerizationconditions comprise a weight hourly space velocity of from about 0.1hr⁻¹ to about 4.0 hr⁻¹.
 16. The process according to claim 1, whereinsaid oligomerization conditions comprise a weight hourly space velocityof from about 0.2 hr⁻¹ to about 3.0 hr⁻¹.
 17. The process according toclaim 1, wherein said oligomerization conditions comprise a weighthourly space velocity of from about 1.75 hr⁻¹ to about 2.25 hr⁻¹. 18.The process according to claim 1, wherein said C₁₂+ fraction has anaverage of from about 0.8 to about 2.0 C₁-C₃ alkyl branches per carbonchain.
 19. The process according to claim 1, wherein said C₁₂+ fractionhas an average of from about 0.8 to about 1.3 C₁-C₃ alkyl branches percarbon chain.
 20. A method for producing a long chain alcohol mixturecomprising contacting the C₁₂+ fraction produced by the process of anypreceding claim with carbon monoxide and hydrogen under hydroformylationconditions and in the presence of a hydroformylation catalyst.
 21. Amethod for producing an alkylaromatic compound comprising contacting anaromatic compound with the C₁₂+ fraction produced by the process ofclaim 1 under alkylation conditions and in the presence of an alkylationcatalyst.
 22. A method for preparing an alkylaryl sulfonate bysulfonating the alkylaromatic compound produced by the method of claim21.